US Airways’ pilots union took its merger integration concerns to federal court last week, suing American Airlines, US Airways and American’s pilots union.

In the lawsuit, the US Airline Pilots Association said the parties cannot agree on a process to determine the seniority integration of the two pilot groups and asked that it be determined by a federal arbiter.

“USAPA seeks declaratory and injunctive relief in the parties’ dispute concerning the integration of seniority lists between the pilots of American and the pilots of US Airways under the McCaskill-Bond Amendment,” the lawsuit said.

McCaskill-Bond is a federal law passed by Congress in 2007 after integration issues between unions at American and TWA. In that merger, TWA employees were placed toward the bottom of seniority lists and were later furloughed during an economic downturn.

According to the filing, the Allied Pilots Association, which represents American’s pilots, and the two airlines filed grievances with the National Mediation Board in late February, saying McCaskill-Bond does not apply to the dispute.

“The defendants have conclusively asserted a position that they are not obligated to comply with Section 13(a) in resolving the seniority list integration dispute,” the suit said.

American declined to comment on the lawsuit.

In dueling messages sent to pilots in mid-February, the two pilots unions argued publicly over the process of developing a seniority integration list.

USAPA said the APA wanted to change the process on how the two unions discuss creating a seniority list. APA shot back saying that the accusation is “misguided” and adding that its position on negotiations between the pilot groups and American’s management has been consistent.

APA has also filed for single-employer status with the National Mediation Board as the two unions had previously agreed, and at some point APA will become the legal representative for both groups.

“If APA is later named the new collective bargaining agent for all pilots, their language would give APA and the Company the right to modify the protocol agreement and override the agreements made with USAPA,” that union said in its message.